Control means for internal-combustion-operated free-piston machines



June 14, 1949. E. s. 1.. BEALE CONTROL MEANS FOR INTERNAL-COMBUSTION-OPERATED FREE-PISTON MACHINES Filed June 20, 1944 5 Sheets-Sheet 1 mm Nnx NYE NTOR. Evd nfiemufi Lomsdowne Beak;

June 14, 1949 E. s. BEALE 2,472,934

CONTROL MEANS FOR INTERNAL-COMBUSTION-OPERATED FREE-PISTON MACHINES Filed June 20, 1944 5 Sheets-Sheet 2 POP w W h AT June 14, 1949. E. s. L. BEALE 2,472,934

CONTROL MEANS FOR INTERNAL-COMBUSTION-OPERATED FREE-PISTON MACHINES Filed June 20, 1944 5 Sheets-Sheet a E NToR. 9 Evelqn Skwqfi lansdounabmdm June 14, 1949. s BEALE 2,472,934

E. CONTROL MEANS FOR INTERNAL-COMBUSTION-OPERATED FREE-PISTON MACHINES Filed June 20, 1944 5 Sheets-Sheet 4 Fig. 4.

E N'TO ra Eve I qn ewm Lonidoume Beale,

June 14, 1949. E. s. BEALE CONTROL MEANS FOR INTERNAL-COMBUSTION-OPERATED FREE-PISTON MACHINES 5 Sheets-Sheet 5 Filed June 20, 1944 .23 5Q UEGBE 46 43.28 0 w m m w w O 7 W m m m o A F23 A 538 wzamz I -I' l l l ll lllllll h FZuu mun- .FZuEuUd EQD u m JOmbZOu JuDk 4b 5b ABSOLUTE DELIVERY PRESSURE: LB/SQW.

Patented June 14, 1949 CONTROL MEANS FOR INTERNAL-COMBUS- TION-OPERATED FREE-PISTON MACHINES Evelyn Stewart Lansdowne Beale,

land, assignor to Alan Muntz &

ited, Hounslow,

Stalnes, Eng- C'ompany Lim- England, a- British company Application June 20, 1944, Serial No. 541,252

In Great Britain June 1, 1943 20 Claims. (Cl. 230-56) This invention relates to lnternal-combustionoperated air-compressors and gas-generators of the tree-piston type.

Such a free-piston machine includes a motor piston and a compressor piston coupled together for operation in unison, this free-piston assembly being unconstrained by any continuously rotatable crank. In a gas-generator, compressed air supplied by the compressor part of the machine is used to scavenge and charge the motor part, which exhausts at superatmospheric pressure, the power gas generated being the mixture of combustion products and excess scavenging air, which may be used, for example, to drive a turbine.

A free-piston machine is started by settin the free-piston assembly at or near the outer limit of its stroke and then accelerating it inwards to compress an air charge in th motor cylinder. Provided the fuel-injection system delivers a charge of fuel into the combustion chamber towards the end of this starting stroke, combustion will take place and the machine will continue to run.

A pneumatic energy accumulator (hereinafter termed a cushion) may be associated with the free-piston assembly, and it takes energy from this assembly during its out-stroke, returning it to the assembly on its in-stroke; the starting stroke is usually efiected by suddenly releasing a predetermined quantity of compressed air into the pneumatic cushion which was previousl at atmospheric pressure, this air serving as the working fluid of the cushion once the machine has started.

It is therefore apparent that starting a freepiston machine involves the performance of a sequence of operations, and that, if for any reason the machine should fail to start at th starting stroke, this sequence of operations must be repeated before a second attempt can be made.

Where a group of two or more free-piston aircompressors or gas-generators are arranged in parallel to feed a common air or gas main, it is often convenient to control all the free-piston machines by a master control system capable of starting and stopping individual machines as is necessary to meet a varying demand for compressed air or power gas. With such a system, failure of any free-piston machine to start in response to a starting impulse from the master controller will disorganise the control of the plant unless special precautions are taken.

Accordingly, an object of this invention is to provide an improved starting control system for a free-piston machine, which is especially suitable for use in a plant comprising two or more free-piston machines and a master controller, and which will provide for accidental failure of the machine to start.

Another object is to provide an internal-combustion-operated air-compressor or gas-generator of the free-piston type with a starting control system adapted automatically to efiect the sequence of operations necessary for starting the machine in response to the actuation of a stopping and starting control member, this system having means which are adapted to cause automatic repetition of said sequence of operations and to be rendered inoperative in response to starting of the machine.

As already mentioned, an internal-combustionoperated gas-generator is usually provided with a cushion; this improves the stability of operation. Nevertheless the possible ranges of variation of delivery pressure and quantity of power gas are usually somewhat limited, and another object of this invention is to provide such a gasgenerator with improved control means which can be operated automatically or at will to suit its output to the demands of a gas-utilising mamachine, such as a turbine.

A further object is to provide control means for a group of such gas-generators feeding a common gas-utilising machine, which can be operated automatically or at will to select the number of gas-generators running at any particular time and to vary the outputs of the individual gas-generators so as to adapt the total rate of generation of power gas to the load on the gas-utilising machine while maintaining the highest practicable overall thermal efiiciency.

Another object is to provide an internal-combustion-operated gas-generator of the free-piston type with a control member or equivalent means for exerting a control influence (e. g. varying fluid pressure) which, on continued displacement or variation in one sense, is adapted first to reduce the quantity of fuel injected into the power-cylinder per cycle while the overall compression ratio is maintained constant or substantially constant at a maximum value, and thereafter to reduce said compression ratio while the 1 quantity of fuel injected per cycle is maintained atlor substantially at its minimum permissible va ue.

The overall compression ratio depends both on the delivery pressure of the gas-generator, which is substantially equal to the pressure in the power cylinder at the instant when the exhaust ports close, and on the travel of the power piston from the point where the exhaust *ports close to the inner dead point of its stroke, and a convenient mode of adjusting the overall compression ratio is to vary the gas-content of the cushion. Accordingly another object of this invention is to provide control means embodying the means for controlling the inner dead point which are described in my patent application Serial No. 492,865, filed June 30, 1943, now U. S. Patent No.

animal 2,470,231, issued May 17, 1949, and which serve to vary automatically the cushion gas-content in dependence on variation of said inner dead point and of the delivery pressure oi the gas-generator.

Another object is to provide, in a gas-generator or the kind in which the delivery stroke oi the compressorpiston coincides with the compression stroke of the power piston, control means capable of varying both the permitted range of variation of the quantity oi. fuel injected per cycle and also the overall compression ratio in such a mannor that a substantially constant cuter dead point of the free-piston assembly is attained as the compression ratio is reduced to its minimum value.

Where two or more gas-generators or the freepiston type supply a common gas-utilising machine imposing a varying demand for gas, the starting or stopping of an additional gas-generator of the group tends to produce a substantial change of working pressure owing to the fact that the minimum output of an individual gas- I generator substantially exceeds zero. Therefore a further object or this invention is to provide, in control means for a group of internal-combustion-operated gas-generators of the free-piston type, which are intended to supply a common gasutilising machine adapted to impose a varying demand for gas, a device capable oi varying the setting of the control member or members 01', or of the means for exerting a control influence on, the gas-generator or gas-generators already or remaining in operation when an additional gas-generator of the group is started or stopped, so as to compensate for the sudden increase or decrease in gas delivery due to that gas-generator. When only one or two gas-generators of such a group are operating, it may be desirable in certain ranges of load to blow some oi the power gas to waste, owing to the fact, hereinbefore reierred to, that the minimum output of a gasgenerator substantially exceeds zero; and 'another object of this invention is to provide in the control mechanism of such a group of gasgenerators automatic means which are adapted to control a blow-oil! valve in such a manner that the control characteristics are suited to the number of gas-generators in operation. Further objects and advantages of the invention will be apparent from the following description of an embodiment of the invention, given by way of example as applied to a group of three gas-generators arranged to feed a turbine through a common manifold. and with reference to the accompanying diagrammatic drawings, in which:

- Fig. 1 shows the control system for the fuelinjection pumps of any one or the gas generators, Fig. 2 shows other parts of the control system for one gas-generator, including means for starting and stopping it,

Fig. 3 is a graph illustrating on a base of time the mode of operation of the mechanism shown in Fig. 2,

Fig. 4 shows the complete installation with the means for controlling all three gas-generators; and

Fig. 51s a graph illustrating the mode 01 operation of the installation as a whole.

The three gas-generators, which are denoted by GI, G2 and G3 in Fig. 4, areslmilar and are adapted to feed gas to a common manifold I33. which supplies a turbine Iii. These gas-gener ators are provided with similar individual control 4 systems. which are indicated by 108 in Fig. 4 and which form elements oi the group control system as a whole. The individual control system will first be described with reference to Figs. 1, 2 and 3.

Each gas-generator. as shown In Fig. 2, which illustrates gas-generator G2 as an example, is of the known opposed-piston type having a power cylinder I3 and two cylinders iI each of which serves as both acompressor cylinder and a cushion. The inner chambers I! of the cylinders II feed a receiver for scavenging air contained in an engine case I3 and communicating with scavenge ports I4 inthe power cylinder in, and the outer chambers I! of the cylinders II serve as the cushions, for receiving energy from the free-piston assemblies I3 during their out strokes and accelerating them on their in strokes. The free-piston assemblies are connected together by conventional synchronising linkage (not shown). Exhaustports I! in the power cylinder communicate with a gas collector I8 connected by a non-return'valve III and a branch pipe II to the gasdelivery manifold I30. The collector I8 is connected to the engine case I3 by a bypass valve HI adapted to be kept closed by a spring-loaded piston I I! subjected-to the collector pressure. The collector is also fitted with a blowoif valve 29 actuated by an oil-pressure relay 2i controlled by a pressure-responsive device 22.

Each of the cushion chambers ii is adapted to be connected to a starting air chamber 23 by a port controlled by a poppet valve 24. A cylinder 25 having its inner end open to the chamber 23.

.end wall of one of the compressor cylinders I! so as to abut against the piston therein and it also co-operates with a maneuvering interlock valve 3i. Thecushio'ns l5 are connected by a balance pipe 32 provided with an air release valve 33 normally closed by a spring and adapted to be opened by a pneumaticmotor 34.

Referring now to Fig.1, each gas-generator is providedwith two fuel-injection pumps I32 of known type having a rack I33 slidable for varying the quantity of fuel delivered per stroke. The racks are urged by springs I towards the position corresponding to zero delivery, The racks are coupled by links I35 to a two-armed lever I38 which is mounted on a fixed bracket I31 and connected by a preloaded spring link I38 to a racktrigger lever ili engaging the collar I42 and adapted to be displaced to release the spring, and thus set the fuel-pump racks to the no-fuel position, by any desired trip device I.

The rack actuating lever I39 is pivoted to a rod I" which terminates in a roller I working between maximu'mjand minimum ruel-pump stop cams I and III. The rod I" includes a pre- I65 slidable in a slot is displaced only loaded extension spring link I5I which will enable the minimum stop cam I66 to be manually overridden to stop the machine. The rod I41 can be rocked about its connection with the lever I39, so as to displace the stop roller I48 along the stop cams. by a piston I52 working in a servomotor cylinder I53 in dependence on the delivery pressure P0 of the gas-generator, which is applied to a bellows device I54. This device actuates through a restorer lever I56 a piston valve I55 which controls the flow of oil, admitted from a relay oil pressure source ROP, to the cylinder I53.

When the stop roller I48 is in the position corresponding to minimum gas delivery pressure, it is in contact with both cams, so that, in consequence, there is only one possible fuel-pump setting for running at minimum output. The stop cams are fixed to a carrier plate I51 oscillatable about a horizontal axis I58 coincident with the stop roller I48 when in said lowest pressure position. An adjustment for the idling point serving to vary the fuel-pump setting to compensate for changes in engine friction, for example when starting from cold, may take the form of a handor thermostatically-controlled adjustment of the pivot pin of the stop cam carrier plate I51, arranged to allow the outer dead point of the free pistons to be adjusted over a limited range with the stop roller I48 in the idling position. This adjustment, which in the example shown is effected by a lever I59, has a very much reduced efiect when the stop roller is at the highpressure end of the stop cams.

The rack lever I39 is coupled by a link I66 to one end of a two-armed lever I6I pivoted on a fixed bracket I62. A floating lever I63 is disposed more or less parallel to the lever I6I, the two levers being linked at said one end by a bar I64 pivoted to the lever I63 and having a pin I66 in the lever I6I so as to provide a limited degree of lost motion; at the other end the levers I6I and I63 are pivotally connected together by a link I61. The bar I64 is also connected to a main control lever '61, which may be a handle adapted for displacement at will, as well as automatically in a manner which will be hereinafter described. A point I66 on the floating lever I63 corresponding to the pivot of the lever I6I serves as a floating fulcrum which when relative motion occurs between the pin I65 and slot I66 of the lostmotion connection between the two levers I6I and I63. The floating fulcrum I68 is connected to the fuelpump stop cam carrier plate I51 for controlling its position about its fixed pivot I58, by a link I69, a multiplying lever I10, a link I" and a two-armed lever I12 pivoted on a fixed bracket I13 and having a pin I14 engaged in a fork I15 on the plate I51. The link I" may have alternative holes I16 for pivotal connection with the lever I12 whereby the compression-ratio range may be varied. The floating fulcrum I66 is alsoconnected, by a rod I11 which is pivotally connected to the link In, to a device for adjusting the compression ratio at which the gasgenerator operates. This device is part of a system for controlling the inner dead point of the free-piston assembly, as described in my said patent application Serial No. 492,865. The portion of the said device shown in the present Fig. 1

includes a bellows device I18 responsive to the pressure Ps existing in the scavenge air receiver I3 of the gas-generator, a follower mechanism I19 responsive to changes in the inner dead point of the free pistons, and a floating lever I for compounding the responses of the elements I16 and I19 and transmitting the resulting by a rod I8I to control means (not shown) for varying the air content of the cushions of the gas-generator, as described in my said patent application. The ratio of the two arms of the floatin lever I86 is varied by sliding a bearing pin I82 of a roller I83 along a slot I84 the agency of a link I85 connected to the rod I11. The roller I83 co-operates with a crosshead I86 of the dead-centre follower I19 and when it is in the position shown relative to the crosshead the gas-generator operates within its maximum range of compression ratio. As the roller I83 is displaced towards the other end of the crosshead I86, the limits of the compression-ratio range.

are progressively lowered.

The mode of operation of the individual control system as a whole is as follows. Starting with the main control lever 61 urged towards the position shown corresponding to maximum output, the rack lever I39 is in the position yielding the maximum fuel delivery permitted by the maximum fuel-pump stop cam I49 for the instantaneous gas-generator delivery pressure Pp. If this pressure varies, the servo-motor I52, I53 moves the stop roller I 46 along the maximum stop cam I49 which is so shaped as to maintain a predetermined maximum outer dead point of the free-piston assembly. As the main control lever 61 is displaced to reduce the output, the levers I6I and I63 are rocked together, under the action of the fuel-pump rack springs I34, until the stop roller I48 engages the minimum stop cam I50, which is shaped so as to maintain a predetermined minimum outer dead point. So far the compression ratio setting has been maintained at its maximum value, and the stop cam plate I51 has been held stationary. However, on further movement of the main control lever 61 in the same sense, two operations occur simultaneously: firstly, the roller I83 of the inner dead point control system is adjusted so as to cause a continuous reduction in compression ratio; and secondly the fuel-pump stop cam plate I51 is displaced in such a direction as to reduce the fuel delivery to the extent necessary to maintain the outer dead point substantially constant as the compression ratio decreases.

Fig. 2 shows further details of the individual control system, including the starting control mechanism, which comprises an automatic starting repeater valve RV, a starting control valve CV, a maneuvering servo-valve MSV, a starting air valve SAV and a maneuvering air valve MAV. These will be described in turn.

The repeater valve RV has two separate c0- axial piston-valve plungers, 35 and 36 associated with springs 31 and 38 which bias them towards their lowest positions. The upper plunger 36 is rigid with a piston 39 working in a cylinder 40, the lower end of which communicates with the engine case I3 through a non-return valve and with the atmosphere by a leak 42. The ports controlled by the upper plunger are so arranged that, when the plunger is at the bottom and the top of its stroke, pipe union 43 and duct 44 are put into communication with each other througlr ports 45 and 46 respectively, while when this plunger is at an intermediate part of its stroke, the union 43 andv the duct 44 are out 01f, from each other while at the same time the duct 44 is connected to a primary spill port 41. The lower plunger 35 when in its lowest position opens in the lever I86, by

a series spill port 40 between the spill port 41 and a drainage connection 48, and it closes a port in parallel with the ports 45 and 40. when the lower plunger is in contact with the upper plunger and the latter is stopped at the upper limit or its stroke, the port 40 is closed and the port 50 is open to the duct 40. The union 3 is connected to a pipe 228 (Fig. 4) for conveying a starting oil pressure SOP from a stopping and starting valve which will be hereinafter described.

The starting control valve CV has a plunger u biased by a s ring 52 towards its left-hand position and provided with a piston 53 working in a cylinder 54, the outer end of which is connected by a pipe I23 to the duct ll of the starting repeater valve RV and can thus be subjected to starting oil pressure. The valve CV has drain ports 55 and 58, a port 58 connected to the pipe 200 (Fig. 4) that supplies a varying control oil pressure GOP to all the gas-generators from the master controller, ports 59 and 50 connected to the source of relay oil pressure ROP which is maintained at a constant pressure and a connection GI and ports 62 and 83 connected respectively to the two ends of the main control cylinder 84 (shown also in Fig. l) of the gas-generator and to the starting air valve SAV. A branch pipe I20 connects the port 8! to the pressure-responsive device 22 of the blow-oii relay 2|.

The maneuvering servo-valve MSV has a plunger 08 biased by a spring 89 towards its righthand position and adapted to be displaced to the left-hand position by a rod 10 co-operating with the piston 85. A port II is connected to the relay oil pressure line BOP; I2 is a drain port, and a connection I3 communicates with the maneuvering air valve MAV.

The starting air valve SAV has a plunger I4 biased downwards by a spring I5 and adapted to be raised by a piston I6 working in a cylinder 11 the lower end of which is connected by a pipe I8 to the relay oil pressure connection 83 of the starting control valve. A spring-biased pneumatically-operated maneuvering safety catch 18 is adapted to prevent the piston 18 from rising more than a short distance above its lowest position, in which the plunger I4 keeps ports 8| and 82 closed, an a similar starting-pressure catch 80 is adapted to prevent the piston I6 from rising above a position such that the plunger puts the ports 8I and 8 into communication with each other. A drain port is denoted by 83. At the upper end of the plunger I4 is a pivoted finger 84 biased by a spring 85 towards a vertical position and provided with a cam surface 88 co-v operating with a fixed abutment 81 to rock the iinger to the right as the plunger assumes its highest position. A poppet air valve 88 is biased downwards towards its closed position by a spring 89 and is adapted to be raised by the finger 84. Compressed air is supplied by a maneuvering and starting air line AP at constant pressure above the poppet valve 88, and the port 90 of this valve is connected by a duct 9I to the port 8I. A pipe 92, including the maneuvering interlock valve 3|, branches from the duct 9I and leads to the pneumatic motor of the maneuvering safety catch I9. The port 82 is connected both by a pipe 93 to the outer ends of the starting valve cylinders 25 and also by a pipe 94 to a restriction 95 opening into the lower end of a bore 98 in which the lower plunger 35 of the repeater valve RV operates. The pneumatic motor of the catch 80 is connected by a pipe I22 to the starting air chambers 23. The maneuvering air valve MAV has a piston 8 01 working in a cylinder 98 and biased towards its lowest position by a spring 99. The lower end of the cylinder 98 is connected by a pipe I02 to the relay oil pressure connection II of the maneuvering servo valve MSV. A rod I00 rigid with the piston 91 carries at its upper end a pivoted finger IOI biased by a spring I02 towards a vertical position. A spring-loaded pneumatically operated trip I04, connected by a pipe I05 to a port I05 in the maneuvering cylinder 28, is adapted to rock the finger IM to the right. A piston valve I01 has a poppet head I08. When the poppet head I08 is on its seat, connection I09 is closed and the piston valve I01 opens an exhaust port H0. A spring III biases the valves I01 and I00 towards their lowest position. Compressed air from the line AP is supplied above-the poppet valve I08; its connection I09 communicates through a restriction I12 and a pipe II3 to the right-hand end of the maneuvering cylinder 28, and through a'pipe H4 and a restriction II5 to the pneumatic motor of the cushion air release valve 33. The pipe H3 is connected through a restriction II8 to the exhaust port H0.

The mode of operation is as follows. The parts are shown in Fig. 2 in the position corresponding to full load. When the gas-generator is brought to rest and the starting oil pressure SOP drops to atmospheric, cylinder 50 of the starting control valve CV exhausts through duct 44 and port 45 of repeater valve RV, and plunger SI of valve CV moves to the left; the control oil pressure COP is shut off at port 58, and connection BI is opened to drain port 55. Consequently pressureresponsive device 22 of blow-off relay 2i is unloaded, this relay holds blow-ofi valve 20 open and gas-collector I8 is therefore exhausted to atmosphere. Engine case I3 is also exhausted, since by-pass valve II8 opens as the collector pressure falls.

Connection 63 of starting control valve CV is also opened to drain port 56, and plunger Id of starting air valve SAV therefore drops to its lowest position. The relay oil pressure is applied from line ROP through port 59 and connection 02 of the starting control valve to the right-hand end of control cylinder 84, so that control lever 81 is moved to its stop position. Piston 55 moves plunger 88 of maneuvering servo valve MSV to the left, so that relay oil pressure ROP acts through port II, connection I3 and pip I03 to raise piston 91 of maneuvering air valve MAV. Thereupon finger IOI raises valve I01, I08, so that exhaust port H0 is shut and air passes through connection I09 to cushion air release valve cylinder 34 and maneuvering cylinder 28. The releas of the engine case pressure has allowed air under pressure in the compressor chambers I2 to escape through the delivery valves. and the pressure in the cushions is released through the cushion air release valve 33 at such a rate that the free-piston assemblies move towards each other; this avoids any risk that the air in the compressor chambers might move these assemblies outwards beyond their correct starting positions.

Maneuvering piston 29 now operates to move :the free-piston assemblies outwards to their starting positions, and when piston 29 uncovers port I08, compressed air from maneuvering cylinder 28 passes through pipe I05 and operates trip I04, so that finger IN is moved to the right, allowing valve I01, I08 to drop and open exhaust port IIO. Cushion air release valve 33 accordin ly shuts. and maneuvering piston 29 is returned 9 by its spring to the right-hand position, so that maneuvering safety valve 3| is opened.

The starting operation will be described with reference to Fig. 3, which shows, on a base of time:

Curve I-starting oil pressure on pipe I23.

Curve II-starting air pressure at ports 82 of valve SAV.

Curve III-pressure in engine case l3 if gas-generator fails to start.

Curve IVpressure in engine case I3 if gas-generator starts.

Curve V-lift of upper plunger 36 of valve RV if gas-generator fails to start.

Curve VAmodiflcation of curve V if gas-generator starts.

Curve VIlift of lower plunger 35. of valve RV.

Curve VII-opening of either of main supply ports 45 and 46 of valve RV if gas-generator fails to start.

Curve VIIA-modification of curve VII if gasgenerator starts.

Curve VIII-opening of primary spill port 41 of valve RV. I

Curve IXopening of parallel supply port 58 of valve RV.

Curve X-opening of series spill port 48 of valve RV.

When the master control operates, in a manner to be hereinafter described, to restart the gas generator at time (a) in Fig. 3, it applies the starting oil pressure SOP to connection 43 of repeater valve RV. When plunger 14 of starting air valve SAV was in its highest position, bore 36 of repeater valve RV was connected through pipe 94 and ports'82 to exhaust port 83, so that lower plunger 35 of valve RV remains in its lowest position. The starting oil pressure is applied through port 45 and duct 84 of valve RV to cylinder 54 of valve CV and moves plunger 5| of the latter to the right.

The control oil pressure COP is applied through port 58 and connection 6| of valve CV, firstly to blow-ofi relay 2i and causes blow-off valve 28 to be shut, and secondly to the left-hand end of control cylinder 64, so that control lever 61 moves to a running position dependent on the magnitude of the control oil pressure, the right-hand end of this cylinder being vented by the drain port 56. At the same time the relay oil pressure is cut oil at port 1! of maneuvering servo valve MSV, since plunger 68 is moved to the right by spring 68, and cylinder 98 of maneuvering air valve MAV is vented by drain port 12, so that piston 91 of valve MAV drops in readiness for the next stopping operation. I

In addition, relay oil pressure is applied through port 68 and connection 63 of valve CV to cylinder 11 of starting air valve SAV and raises piston 16 into engagement with catch 19. Thereupon finger 84 opens poppet valve 88 slightly and admits compressed air from line AP through port 38 to duct 9 I, port 82 still being closed. Air passes from duct 3| through pipe 92, and provided the maneuvering gear is properly set, interlock valve 3! will be open and will pass air to catch 18 which is thus retracted and allows piston 18 to rise into engagement with catch 88. This causes poppet valve 88 to open fully and ports BI and 82 to be put in communication with each other at time (b) in Fig. 3. Compressed air from line AP thereupon passes through pipe 83 to starting air chambers 23 through non-return valves 21 in startingvalve pistons 26, valves 24 being held closed by the air pressure; compressed air also passes, at the time (b) in Fig. 3, through pipe 84, to bore 86 of valve RV and raises lower plunger 35 at a limited speed, owing to the restriction 95. After the clearance between plungers 35 and 36 has been taken up, they rise together to the top of their stroke. During this upward stroke, lower plunger 35 first closes series spill port 48, at time (c) in Fig. 3, and immediately thereafter starts to open supply port 58 and picks up upper plunger 36, which begins to close port 45; however the starting oil pressure connection is maintained through 'valve RV, since as port 45 closes port 58 opens. As soon as upper plunger 36 has closed port 45, at time (d) in Fig. 3, it begins to open primary spill port 41; it then closes spill port 41 again at time (e) and immediately begins to open supply port 46, which is fully open at time (1) when plunger 36 reaches the top of its stroke. Since series spill port 48 is closed before primary spill port 41 opens, there is no loss of starting oil pressure. Both plungers are now in the top position,

and valve RV has not interfered in any way with the application of starting oil pressure to valve CV.

When the air pressure in starting air chambers 23 has risen to the correct value, at time (g), this pressure, transmitted by pipe I22, releases catch 88 and allows plunger 14 of valve SAV to rise to the top of its stroke, abutment 81 thereupon rocking finger 84 clear of valve 88 which shuts. Pressure in starting valve cylinders 25 is released to atmosphere through ports 82 and 83, and valve pistons 26 are thrust outwards by the air pressure in starting air vessels23, opening starting valves 24. The starting air then expands into cushions l5 and drives the free-piston assemblies towards each other. The gas-generator should now start, and, if it does so, the engine case pressure will rise immediately to a value sufilcient to hold piston 33 and upper plunger 36 of valve RV at the top of their stroke. Main supply port 46 is therefore open and primary spill port 41 is shut, so that the starting oil pressure is maintained in a cylinder 54 of valve CV. In the meantime, since port 82 of valve SAV has been opened to atmosphere through port 83, lower plunger 35 of valve RV is returned by spring 31 to the bottom of its stroke.

If, on the other hand, the gas-generator fails to start at time ('0), there will be no sustained engine case pressure, and upper plunger 36 of valve RV will drop under the force of spring 38 at a low speed determined by leak 42. Lower plunger 35, however, drops comparatively rapidly and reaches the bottom of its stroke at time (h), closing parallel supply port 58 and opening series spill port 48. Thereafter upper plunger 38, in its downward travel, closes main supply port 46 at time (i) and then opens primary spill port 41, thereby releasing the starting oil pressure from cylinder 54 of valve CV, plunger 5! of which accordingly returns to its left-hand position ready for another attempt to start.

Top plunger 36 of valve RV falls slowly enough for the maneuvering process to be completed in the manner hereinbefore described, and thereafter, at time (7'), it closes primary spill port 41 and reopens main supply port 45. Thereupon plunger 5| of valve CV is again moved to the right, and the starting operation is repeated, exactly as at the first attempt, except that lower plunger 35 of valve RV begins to rise before upper plunger 36 has reached the bottom of its stroke; but this has no eflec't on the operation,

11 as upper plunger -38 is met at time (m) by lower plunger 35 and lifted as before.

The master control gear, shown in Fig. 4, is

arranged to actuate in unison the main control levers 01 of the three gas-generators in response to displacement of a master control lever, which may be hand operated, but which in the present example is actuated by a governor I81 of the turbine I3I. The master control gear also starts and stops individual gas-generators as is necessary to accommodate the plant to a varying load.

As already mentioned, each of the gas-generators is provided with an individual gas-collector chamber I8 connected to the common gas manifold I30 by a gas-outlet valve II1 which is in effect, a non-return valve, but which is conveniently operated by an oil servo-motor controlled by a difierential device responsive to collector pressure, and manifold pressure. The servo-motor consists of a piston I88 working in a cylinder I89; a piston valve I90, which controls the supply of oil from the relay oil pressure source ROP to either end of the cylinder I89, is actuated by a piston |9I working in a cylinder I92 and loaded by a spring I93. Gascollector pressure is applied to one end of the cylinder I92 through a pipe I94 and acts on the piston in opposition to the spring, while manifold pressure is applied to the other end of the cylinder through a pipe I95. When the gas-collector pressure falls to manifold pressure, the spring I93 ensures that the valve I I1 is kept shut; when the gas collector pressure exceeds the manifold pressure sufliciently to displace the piston I9I against the spring force, the valve I I1 opens.

The control oil pressure COP applied to pipe 200 is determined by a mechanism consisting basically of an automatic control. oil pressure regulator composed of a bellows responsive to control oil pressure, a valve for varying the control oil pressure and a restorer lever. 'The setting of this regulator is determined by the position of the input point of the restorer lever, and this setting is controlled by a bellows responsive to delivery pressure Pp. This combination constitutes a regulator for the delivery pressure, the setting of which can be adjusted by means of a master control lever. The said valve is a balanced piston-type valve 'Il99 adapted to connect the control oil pressure main 200 alternatively to a source of oil at constant pressure, e. g. the relay oil pressure source ROP, and to exhaust. The valve I99 is actuated by a. differential lever I connected to a bellows device 202 responsive to control oil pressure and to a second difierential lever 203 which is connected to a variable-datum device I98 through a lever 204 and to a third differential lever 205, the lever 205 being connected to the working pressure bellows I91 and to the master control lever I96. The arrangement is such that, if the delivery pressure PD in the manifold, I falls, the valve I99 is displaced to the right so as to increase the control oil pressure and thereby cause the individual main control levers 61 of the gas-generators to be moved so as to increase the rate of fuel supply. The master control lever I96 has the efiect of altering the setting of the working pressure bellows I91.

, The working pressure bellows is of the springloaded type, housedin a gas-tight casing communicating with the manifold by a pipe 205. In order to secure at the same time high sensitivity and stability of operation of the master control gear, the duct connecting this casing to the manifold may be controlled by a needle valve 201 actuated bythe bellows. This needle valve is so arranged as to decrease the degree of throttling with increasing working pressure atleast over the middle and lower part of the working pressure range.

The object of the variable-datum device I9. is to assist the working pressure bellows l9! to maintain a constant delivery pressure when a gas-generator is started or stopped, and for this purpose it is arranged to be responsive to the starting and stopping of the delivery of gas from the gas-generator to the common manifold. The preferred arrangement shown employs the response of the gas-outlet valves II'I. Accordingly the device I98 is provided with two cylinders 200 and 209 connected respectively by pipes 2Il and 2 with the servo-motor cylinder I89 of the gas-generators G2 and G3 in such a manner that the relay oil pressure, when it is applied to either of these cylinders I89 to open the gas delivery valve III, also energises the cylinder 208 or 209 communicating therewith. The device I98 also includes a slidable bar 2I2 pivotally connected to the lever 204 and urged to the right by a compression spring 2l2. A crosshead 2 fast on the bar 2I2 co-operates with a short plunger H5 and a long plunger 2I6 having limited degrees of sliding movement respectively in the cylinders 208 and 209. The bar 2I2 and lever 204 can thus assume three predetermined positions: first, that shown when both cylinders 208 and 209 are energised and the long plunger 2I6 controls the position of the crosshead; second, an

intermediate position where only the cylinder 209 is energised and the short plunger 2l5 locates the crosshead; and third, the extreme right-hand position where --both cylinders 208 and 209 are de-energised and the crosshead is held against a stop ZII by the spring 2 I3. The variable-datum device thus operates to move the fulcrum of the difierential lever 203 by a distance appropriate to correct the control oil pressure and hence the setting of the main control levers 61. Thus, when an additional gas-generator,-for example, starts,- the fuel supply ofall the gas-generators operating is abruptly reduced so as to compensate for the additional source of power gas, without any change in the setting of the master control lever I96 or any motion of the working pressure bellows I91 other than that due to a relatively slight final correction. I

The gas-generator GI is the first to be started and the last to be stopped, while the gas-generator G2 is the next to be started as the load rises and is stopped next before GI as the load falls. The servo-motor 2| controlling the blowofl. valve 20 of gas-generator G2, as already described with reference to Fig. 2, is controlled by the bellows device 22 which is adapted to be energized by the control oil pressure applied through the pipe I20. The servo-motor includes a piston 2I8 counpled through a crank lever 2I9 to the valve 20 and operating in a cylinder 230 to the ends of which oil from the relay oil pressure source is admitted alternatively by a valve 220 controlled by a restorer lever 22I coupled to the bellows device 22 and deriving a return motion from the piston 2l8.' The servo-motor 2| 0! a the gas-generator G3 is similar to that of the gas-generator G2. The servo-motor 2IA controlling the blow-off valve of the gas-generator GI is again-similar to the servo-motors 2I with the exception that its restorer lever 22I is controlled by two oil'pressure responsive bellows 22 and 22 actlng'in opposition. .The bellows 22 are.

energized by relay oilpressure controlled by the 9 13 individual control system 108 of the gas-generator GI, while the bellows 222, which have a smaller efiective area than the bellows 22, are Subjected to the control oil pressure in the individual control system of the gas-generator G2, this pressure being taken oil? the pipe I20 of gasgenerator G2 by a branch 223.

The master control lever controls three starting-and-stopping valves which respectively control the three starting 'oil pressure circuits of the three gas-generators. These valves are shown diagrammatically as combined in a rotary v distributing valve 224 connected to the shaft oi the master control lever I96 .by a driving coupling providing a small degree of lost motion, indicated at 229. This provides a margin for increase of load, after a gas-generator has been stopped, before it is required to be started again. In the position shown, the valve 224 puts the source of relay oil pressure ROP into communication with three pipes 225, 226 and 221 which connect to the starting oil pressure ports 43 (Fig. 2) of the repeater valves RV of the three gas generators GI, G2 and G3 respectively. As the master control lever I96 is displaced in a counter-clockwise direction, the pipes 22I, 226 and 225 are successively and in this order disconnected from the source ROP and put into communication with a drain port 228.

The mode of operation of this plant will be described with reference to Fig. 5, which represents the characteristic of each gas-generator by a family of curves on a graph having heat in fuel per cycle (which corresponds to displacement of the fuel-pump racks I33 in Fig. 1) as ordinate (left-hand scale) and absolute delivery pressure PD of the gas as abscissa. For convenience of description, the rack displacement will be referred to as a, percentage of full-load displacement from the zero delivery position at the origin, and the gas pressure will be assumed to rise to 71 lb./sq. in. abs. at full load. The uppermost curve I of the family corresponds to an overall compression ratio of 16:1 and maximum outer dead point. The fuel-pump stop cams I 49 and I56 (Fig. 1), as already explained. are shaped to give only one possible setting at idling, and consequently the lower end of curve I droops slightly to a common point Q at 27% fuel and atmospheric pressure. Curves II. III and IV correspond respectively to overall compression-ratio settings of 16:1, 12:1, and 10:1 respectively and to minimum outer dead point. The lower end of curve IV below about 21 lb./sq. in. pressure drops less steeply to the common point Q. Curve V shows the turbine power characteristic, the percentage power output being given by the shorter righthand ordinate scale.

The operations involved in varying the load from full to stop and back again to full will now be described. Starting at full load with all three gas-generators running, initial displacement of the master control lever I96 from the position in which it appears in Fig. 4 reduces the working pressure from 71 to 47.5 lb./sq. in. along chaindotted track ABCE, the turbine output dropping to 43%.

The longer right-hand ordinate scale represents control oil pressure COP of the master control gear as a percentage of the maximum value, and for convenience of description this scale has been so chosen that the track AB represents both rack position and control oil pressure. When the compression ratio setting is changed, for example over the range BE, the main control lever 61 of each gas-generator has to change not only the 14 fuel-pump setting, but also the compression ratio setting, so that the dotted line BE representing the control oil pressure over this range is steeper than the line BE.

In order to reduce the load further, gas-generator G3 must be stopped, and this is done by the stopping and starting valve 224 which is actuated by the master control lever I96 as it moves into the position corresponding to the delivery pressure of 47.5 lb./sq. in. to connect pipe 221 to the drain 228. As a result, the main control lever 61 of gas-generator G3 is moved by its main control piston 65 into the stop position, and the individual control system operates, as hereinbefore described with reference to Fig. 2, to maneuver the free pistons of this gas-generator into their starting position. Gas-generators GI and G2 must now carry the load, and the variable-datum device I98 operates, as delivery of gas by gas-generator G3 ceases and causes the cylinder 209 of the variable-datum device to be de-energised, to set them at point F, i. e. in the range of constant maximum compression ratio setting. The load is still further reduced, and, when the pressure denoted by points H and H is reached, along the tracks FGH for fuel-pump rack setting and FGH for control oil pressure, the compression ratio being now at its minimum working value, the blow-off valves 20 of gas-generators GI and G2 begin to open under the influence of their blow-off relays 2IA and 2|. As the control oil pressure drops from H to K and the delivery pressure from H to K along curve IV, each blow-off valve opens gradually wider under the influence of the falling control oil pressure, the rates and initial loadings of the bellows springs being so selected that the two blow-oil? valves operate similarily. During this time the compression-ratio setting remains at the minimum of 10:1, as determined by the lost motion between the pin I65 and the slot I66 (Fig. 1). The fuel-pump rack setting is also that determined by the minimum fuel-pump stop cam I50, but as the delivery pressure falls, this cam recedes, allowing the rack setting to'be further reduced.

To reduce the load below 26 lb./sq. in., gasgenerator G2 is stopped by means of the stoppingand-starting valve 224 which connects pipe 226 to the drain 228, and the variable-datum device I98 thereupon operates, on de-energising of its cylinder 208, to step up the control oil pressure from K to L. As the load is still further reduced, blowing-off must start again at the points N, N,

, when the control oil pressure has dropped to 46%,

which is much lower than at the point H; for

this reason the settin of the blow-off relay 2IA has been altered by putting out of action the smaller bellows 222 owing to its connection to the control oil pressure applied through the individual control system of the gas-generator G2. When the minimum delivery pressure is reached with the blow-ofi valve 20 wide open, final movement of the master control lever I96 actuates the stopping-and-starting valve to stop gas-generator GI by connecting its pipe 221 to drain.

The process of starting the gas-generators and bringing them succesively on load is largely a reversal of the above described sequence, but there are some aspects that will be further discussed.

The procedure in changing from stop to full load is then briefly as follows.

When gas-generator GI is started by movement of the master control lever I96 from the stop position, the blow-off valve 20 of this gas-generator will be open because the control oil pressure is 15 very low unless the master control lever has been moved too far. With the blow-off fully open there will be an excess pressure in the gas collector I8 of about 1.5 lb./sq. in., so that the gas outlet valve I I! will open and some gas will pass to the turbine. If the master control lever is moved slowly so that a the gas pressure is kept to its equilibrium value,

then the track followed on Fig. will be the reverse of that described when stopping, i. e. QQ', NN', M, L, but from there it will go to J before gas-generator G2 is started, owing to the backlash, indicated at 229 in Fig. 4, provided between the valve 224 and the lever 96.

On the other hand, if this lever is moved immediately up to the position corresponding to steady running at the point J, the control oil pressure rises to a high value because the gas pressure is temporarily lower than that corresponding to this position. Therefore the blow-oil" valve closes rapidly, instead of remaining open over the range QN, and also the high control oil pressure will push the main control lever 61 of gas-generator GI over to th top limit, i. e., putting the compression ratio setting at maximum (16:1) and the stop roller 48 against the maximum fuel cam I49, giving the maximum outer dead point. Thus in this case the track will go from Q along the upper limit curve to J, the control oil pressure being indeterminate but high, approximately equal to the full relay oil pressure to start with, and falling of course to the equilibrium value at J.

Proceeding slowly upwards from point J by moving the master control lever I96 a very small amount, the stopping and starting valve 224 operates to start gas-generator G2, and the degree of opening of its blow-oil valve 20 is gradually reduced, raising the pressure in its gas collector I8 to the manifold pressure, namely 26.5 lb./sq. in. During this time the control oil pressure will be at J (19), so that th compression ratio setting and fuel will be at maximum, and the track of gasgenerator G2 will be along the upper limit curve I of Fig. 5 from Q to J with the whole output from gas-generator G2 blowing oiT.

As the blow-01f valve of gas-generator G2 closes further, the gas-outlet valve H1 of this gas-generator opens, and gas in increasing quantity is delivered to the manifold. The master control in its role of gas-pressure controller, in order to keep the delivery pressure constant, reduces the control oil pressure, thereby opening the blow-off valve on gas-generator GI, and this therefore follows the vertical track from J to P. Both gasgenerators GI and G2 are now working at the point PP with a control oil pressure of about Proceeding upwards slowly, both gas-generators follow the track PP, HH, G, F, and then on to point D.

If, on the other hand, the master control is moved immediately from point J to a position cor,- responding to point D, the control oil pressure -will be high, approximately at full relay oil pressure, so that, as soon as gas-generator G2 starts to deliver gas, both gas-generators follow the top limit curve I from J to D, i. e. gas-generator Gi does not blow-oil at all, and point D is reached when the blow-oil valve of gas-generator G2 has closed fully.

The process of starting up gas-generator G3 and bringing the set on to full load at point A is exactly similar to that described above, except that as G3 comes in, GI and G2 do not blow off as the point C is well above the lower limit curve 'lne variable-datum device I88 should ideally have a time constant equal to that of the control or operation which it is required to compensate. Consequently the characteristics of the re turn spring or springs and the flow-capacities of the connections to the cylinders 208 and 209 are so chosen as to give time constants which will avoid or reduce temporary errors in speed or delivery pressure.

I claim:

1. An internal-combustion-operated free-piston machine having a free-piston assembly, starting mechanism including means for maneuvering said assembly to a starting position adjacent to one limit of its stroke, means for accelerating said assembly from said position towards the other limit of its stroke, and a starting control member operable to cause at least both said means to operate in the sequence necessary to start the machine, repeater means operatively associated with said starting mechanism for causing automatic repetition of said sequence, and means responsive to starting of the machine for rendering said repeater means inoperative.

2. An internal-combustion-operated free-piston machine having a free-piston assembly and including automatic starting means serving' to effect, in response to release therefrom and application thereto of a. starting fluid pressure, a sequence of operations which are necessary to start the machine and which include maneuvering said assembly to a starting position adjacent to one limit of its stroke and accelerating the assembly from said position towards the other limit of its stroke, a control valve operable for applying and releasing said pressure to and from said means, repeater means serving to cause automatic repetition of said sequence of operations, said repeater means including a repeater valve which in one condition connects said control valve to said automatic starting means, which in a second condition releases said pressure from said automatic starting means, and which is so biased that it tends to assume said second condition in response to application of said pressure to said automatic starting means and after a predetermined time lag to revert to said one condition, and means responsive to starting of the machine for maintaining said repeater valve in said one condition.

3. An internal-combustion-operated free-piston machine having a free-piston assembly including a pump piston, a receiver arranged to be charged by said pump piston, a starting control member operable to cause at least both said means to operate in the sequence necessary to start the machine, repeater means operatively associated with said starting mechanism for causing automatic repetition of said sequence, and means responsive to increase of pressure in said receiver for disabling said repeater means.

4. An internal-combustion-operated free-piston machine including automatic starting means capable, in response to release therefrom and subsequent application thereto of a starting fluid pressure, of effecting a sequence of operations which are necessary to start the machine and which include maneuvering said assembly to a starting position adjacent to one limit of its stroke and accelerating the assembly from said position towards the other limit of its stroke, a. control valve operable for applying and releasing said pressure to and from said means, a starting repeater valve connected between said control valve and said automatic starting means, said 17 repeater valve including a first closure member which is biased to one end position, which puts said control valve in communication with said starting means when in both end positions, and which prepares to release said pressure from said starting means when in an intermediate position, means for overcoming the bias on said closure member in response to starting of said machine, and a second closure member which is biased to one end position in which it co-operates with said first closure member to release said pressure from said starting means, which puts said control'valve in communication with said starting means when displaced from said one end position, and which is capable on such displacement of shifting said first closure member against its bias, and means responsive to application of said pressure to said starting means for displacing said second closure member to its other end position and thereafter permitting it to return to its first end position.

5. An internal-combustion-operated free-pis ton machine including automatic starting means capable, in response to release therefrom and subsequent application thereto of a starting fluid pressure, of effecting a sequence of operations which are necessary to start the machine and which include maneuvering said assembly to a starting position adjacent to. one limit of its stroke and accelerating the assembly from said position towards the other limit of its stroke, a control valve operable for applying and releasing said pres-sure to and from said means, a starting repeater valve connected between said control valve and said automatic starting means, said repeater valve having two relatively movable closure members each associated with a fluid pressure motor and co-operating, firstly on energizingnf one of said motors, to maintain said control valve in communication with said starting means, secondly, on subsequent energising of the other of said motors and de-energising of said one motor also to maintain such communication, and alternatively, on de-energising of said one motor without energising of said other motor, of releasing said pressure from said starting means, means for energising and subsequently de-energising said one motor in response to application of said pressure to said starting means, and means for energising said other motor in response to starting of said machine.

6. An internal-combustion-operated gas-gen-v erator of the free-piston type including a power cylinder, a free-piston assembly cooperating with said cylinder, means for injecting fuel into said cylinder, a fuel-control member operable for varying the quantity of fuel injected per cycle, a compression-ratio control member operable for varying the overall compression ratio of the working fluid in said power cylinder, and main control means operatively associated with said control members in such a manner that on continued variation of said main control means in one sense first the fuel-quantity is reduced while said compression-ratio is maintained substanvarying the quantity or fuel injected per cycle and biased towards the position yielding minimum fuel-delivery, a compression-ratio control member operable for varying the overall compression ratio or the working fluid in said power cylinder, a common control member, an operative connection including a lost-motion device between said common control member and said fuel-control member, and means responsive to relative displacement of the elements of said lost-motion device for actuating said compression-ratio control member in such a sense as to reduce the compression-ratio as said common control member approaches the end of its range of travel yielding minimum output.

8. An internal-combustion-operated gas-generator of the free-piston type'including a. power cylinder, a free-piston assembly cooperating with said cylinder, means for injecting fuel into said cylinder, a fuel-control member operable for varying the quantity of fuel injected per cycle, a compression-ratio control member operable for varying the overall compression ratio of the working fluid in said power cylinder, a common control member, an operative connection between said common control member and said fuel-control member arranged to give a ratio oiflvelocity of displacement of said common control member to that of said fuel-control member, which is higher over the lower part of the power-output range than over the higher part thereof, and a connection operative between said common control member and said compression-ratio control member substantially. only over said lower part of the power-output range. i

9. A free-piston internal-combustion-operated gas-generator having a compressor cylinder, a power cylinder, a free-piston assembly of a compressor piston and a power piston co-operating with said cylinders respectively, the gas-generator being of the kind in which the delivery stroke or its compressor piston coincides withthe compression stroke of its power piston and including tially constant at a maximum value and thereafter said compression-ratio is reduced while the fuel-quantity is maintained substantially at its minimum permissible value.

7. An internal-combustion-operated gas-generator of the free-piston type including a power cylinder, a free-piston assembly cooperating with said cylinder, me ans for injecting fuel into said cylinder, a fuel-control member operable for a fuel-control member operable for varying the quantity or fuel injected into its power cylinder per cycle, a compression-ratio control member operable for varying the overall compression ratio oi the working fluid in the power cylinder, and an adjustable device which serves for varying the permitted range of displacement of said fuelcontrol member, said device being so interconnected with said compression-ratio control member that as the compression ratio is reduced to its minimum value while said fuel-control member is maintained at the lower limit or the varying range permitted by said device, the outer dead point of the free-piston assembly of the gasgenerator remains substantially constant.

10. A free-piston internal-combustion-operated gas-generator having a power cylinder, a compressor cylinder, a free-piston assembly cooperating with said cylinders in such a manner that the delivery stroke of the compressor piston coincides with the compression stroke of the power piston,- means for injecting fuel into said power cylinder, 9, fuel-control member for varying the fuel-quantity injected per cycle, a compression-ratio control member for varying the overall compression ratio of working fluid in said power cylinder, an adjustable device capable oi varying the permitted range of displacement of said fuel-control member, means responsive to variation in the gas-delivery pressure of the as-- erative connection between said compressionratio control member and said adjustable device for varying the absolute value of the lower limit of said range in such a manner as to reduce variation in the outer dead point of said free-piston assembly consequent on displacement of said compression-ratio control member.

11. A free-piston internal-combustion-operated gas-generator having a power cylinder, 8, compressor cylinder, a free-piston assembly co-operating with said cylinders in such a manner that the delivery stroke of the compressor piston coincides with the compression stroke of the-power piston, means for injecting fuel into said power cylinder, at fuel-control member for varying the fuel-quantity injected per cycle, a compressionratio control member for varying the overall compression ratio of working fluid in said power cylinder, an adjustable device capable of varying the permitted range of displacement of said fuelcontrol member, means responsive to variation in the gas-delivery pressure of the gas-generator for adjusting said device so as to vary at least the magnitude of said range, a common control member, means biasing said fuel-control member towards the position yielding minimum fuelquantity, an operative connection including a lost-motion coupling between said common control member and said fuel-control member, means responsive to relative displacement of the elements of said lost-motion coupling for actuating said compression-ratio control member in such a sense as to reduce the compression ratio as said common control member approaches the end of its range of travel yielding minimum output, and an operative connection between said compression-ratio control member and said adjustable device for varying the absolute value of the lower limit of said range in such a manner as substantially to eliminate variation in the outer dead point of said free-piston assembly consequent on displacement of said compressionratio control member.

12. A free-piston internal-combustion-operated gas-generator having a power cylinder, a com pressor cylinder, 2, free-piston assembly co-operating with said cylinders in such a manner that the delivery stroke of the compressor piston coincides with the compression stroke of the power piston, means for injecting fuel into said power cylinder, a fuel-control member for varying the fuel-quantity injected per cycle, a compressionratio control member for varying the overall compression ratio of working fluid in said power cylinder, maximum and minimum fuel-quantity cams, a cam-follower co-operating with said cams and connected to said fuel-control member for limiting displacement thereof, means responsive to gas delivery pressure for displacing said camfollower relatively to said cams in a sense such as to vary both the range and the absolute value of the limits of displacement of the fuel-control member, means responsive to displacement of said compression-ratio control member for displacing said minimum fuel-quantity cam relatively to said cam-follower in such a sense as to reduce the minimum fuel-quantity as the compression ratio is lowered, means biasing said fuel-control member towards its position yielding minimum fuel delivery, a common control member, a lost-motion coupling between said common control member and said fuel-control member, and means responsive to lost motion in said coupling for actuating said compression-ratio control member in such a sense as to lower the compression ratio as said common control member approaches the position corresponding to minimum power output.

13. A group of internal-combustion-operated gas-generators of the free-piston type connected to supply a common gas-utilising machine adapted to impose a varying demand for gas, each of said gas-generators having an individual control system including a main control member and operable for varying its power output in response to displacement of said main control member, and said group having a master control system including means for actuating saidmain control members, a variable-datum device capable of varying the setting of said means so as to vary the output of those of said gas-generators already in or remaining in operation when an additional gas-generator of said group is started or stopped respectively, and means responsive to the delivery of gas by said additional gas-generator for automatically adjusting the setting of said variable-datum device so as at least in part to compensate for the tendency of the gas-delivery pressure to change as a result of such starting and stopping.

14. A group of internal-combustion-operated gas-generators of the free-piston type connected to supply a common gas-utilising machine adapted to impose a varying demand for gas, each of said gas-generators having an individual control system including a main control member and operable for varying its power output in response to displacement of said main control member, and said group having a master control system including means for actuating said main control members, a variable-datum device capable of justing the setting of said variable-datum device so as at least in part to compensate for the tendency of the gas-delivery pressure to change as a result of such starting and stopping.

15. A group of internal-combustion-operated gas-generators of the free-piston type connected to supply a common gas-utilising machine adapted to impose a varying demand for gas, each ofsaid gas-generators having an individual control system operable for varying its power output in response to variation of a control fluid pressure, and said group having a master control system including a control fluid pressure main, a master control member, a device responsive to said control fluid pressure, a device responsive to the delivery pressure of the gas supplied to said machine, a variable-datum device and a two-way valve for connecting said control fluid pressure main alternatively to a source of fluid at superatmospheric pressure and to a reservoir for fluid at a pressure lower than that of said source, said master control member, said three devices and said valve being difierentially connected together, and means responsive to the starting or stopping of at least one gas-generator of said group for automatically adjusting the setting of said variable-datum device so as at least partly to compensate for the tendency of the gas delivery of the group to increase or decrease suddenly when said one gas-generator is started or stopped.

16. A group of internal-combustion-operated 21 gas-generators of the free-piston type connected to supply a common gas-utilising machine output in response to variation of a control fluid pressure, an automatically opening delivery valve between at least one of said gas-generators and said common machine, said group having a master control system including a control fluid pressure main, a master control member, a devic responsive to said control fluid pressure, a device responsive to the delivery pressure of the gas supplied to said machine, a variable-datum device ,and a two-way valve for connecting said control fluid pressure main alternatively to a source of fluid at superatmospheric pressure and to a reservoir for fluid at a pressure lower than that of said source, said master control member, said three devices and said valve being difierentially connected together, and means responsive to the operation of said delivery valve for automatically adjusting the setting. of said variable-datum device so as at least partly to compensate for the tendency of the gas-delivery of the group to increase and decrease suddenly when said one gas-generator is started and stopped.

17. A group 01' internal-combustion-operated gas-generators of the free-piston type connected to supply a common gas-utilising machine adapted to impose a varying demand for gas, each of said gas-generators having an individual control system including a main control member and operable for varying its power output in response to displacement of said main control member, a valve for blowing-oil? gas. and automatic means responsive to displacement of said main control member for controlling said blow-oil valve, said group having a master control system including means for actuating said main control members and for starting and stopping individual gas-generators of said group, and means responsive to alteration in the number of said gas-generators in operation for varying the control characteristic of said automatic blow-oi! control means.

18. A group of internal-combustion-operated gas-generators oi the free-piston type connected to supply a common gas-utilising machine adapted to impose a varying demand for gas, each 01' said gas-generators having an individual. control system operable for varying its power output in response to variation of a control fluid pressure, and at least one oi said gas-generators having a blow-ofl valve branched from a supply conduit leading to said gas-utilising machine, and said group having a master control system including means for varying said control fluid pressure to suit the load on said machine, means for starting and stopping individual gas-generators of said group, and two differentially-acting devices responsibe to variation in said control fluid pressure for automatically. and progressively operating said blow-off valve, said starting and trol system operable for varying its power output in response to variation 01' a control fluid pressure and for starting and stopping it in response to application to and release from said system of a starting fluid pressure, and said group having a master control system including a differential mechanism associated with a master control member, with a device responsive to the stopping means serving to de-energise one of said fluid-pressure-responsive devices on stopping of another gas-generator of said group.

19. A group of internal-combustion-operated gas-generators or the free-piston type connected to supply a common gas-utilising machine adapt, ed to impose a varying demand for gas, each of said gas-generators having an individual conpressure of the gas supplied to said machine, with a variable-datum device and with a fluid control valve for varying said control fluid pressure, valve means operatively connected with said master control member for supplying said starting fluid pressure to said individual control systems in succession as said master control member is progressively advanced towards the full-load position, and means responsive to the delivery of gas by one of said group for varying the setting oi said variable-datum device so as to adjust said control fluid pressure to compensate for/such delivery.

20. A gas-generator of the two-stroke compression-ignition free-piston type including a power cylinder having piston-controlled scavenge ports and exhaust ports, a compressor cylinder co-axial with said power cylinder, a free-piston assembly including a power piston working in said power cylinder and a compressor piston working in said compressor cylinder, a scavenge air receiver communicating with said scavenge ports, a delivery valve communicating between said receiver and the end of said compressor cylinder nearer to said power cylinder, an inlet valve opening into the said end. the other end oi said compressor cylinder forming a cushion, a fluid-pressure-actuated valve for exhausting said cushion, a fluid pressure motor for maneuvering said tree-piston assembly to a starting position, means for admitting a charge of starting gas into said cushion, a fluid-pressure-actuated valve for exhausting said receiver, and automatic control means serving when the gas-generator is stopped to open said last-mentioned valve and thereby permit said free-piston assembly to assume under the influence of the cushion pressure a position on the inner side of its starting position, to release the cushion pressure through said cushionexhaust valve and to energise said motor and thus cause it to move said free-piston assembly out to its starting position.

EVELYN STEWART LANSDOWNE BEALE.

REFERENCES CITED The following references areoi record in the 

